Vehicle communication system



jm@ H. G. BUSHGNHES 295W,

VEHICLE oomquNIcATloN SYSTEM Filed Jan. 1e, 194e s sneetssneet E Qi@ d'a l] j IIIIIIHIIIIIIIIIII /3 232 Zm 251 Q50 FROM -w T258 jm@ 9 E5@ H.G. BUSHGNHES 25%,@

mucus c'omUNIcMoN sYs'mu Filed Jan. 16, .1946 8 Sheets-Sheet 2 ifs o51455' SINE 56 M11/.f Gm'. WEST EPM/NAL c//Pcu/r Hime 5 395@ H. e.BUSIGNHES QS@ VEHICLE COMMUNICATION SYSTHG Filed Jan. 16, 1946 8Sheets-Skaai'. 3

T//WE CHAN/VEZ 6 I (aff) ATTORNEY Jun@ @y 3%@ H. G. UsaGNaEs w@ VEHICLEComUNICATION SYSTEM Filed Jan. 16, 1946 8 Sheets-Sheet 5 me N50 H. G.usnGNlEs VEHICLE COMWUNICATION'SYSTEM ATTOPNE Jun@ 69 395@ Filed Jan.16. i946 H. G. EUSHGNBES VEHICLE COMMUNICATIGN SYSTE S Sheetsusheet Z5?l' i jm@ 5 3.95@ H.r G. ausamas gw@ VEHICLE COMMUNICATION SYSTEMv FiledJan. 16, 1946 8 Sheets-Shea?. 3

Patented June 6, 1950 ortica 2,510,068 VEHICLE COIVIMUNICATION SYS-'IEMHenri G. Busgnies, Forest Hills, N. Y., assignor to Federal Telephoneand Radio Corporation,

New York, N.

Y., a corporation of Delaware Application January 16, 1946, Serial No.641,581

47 Claims.

This invention relates to radio communication systems for vehiclesmoving along a fixed route. More particularly it deals with a highfrequency cable and radiating means adapted for multichannel telephoneand signal communications for vehicles such as trains including meansfor indicating the location of the vehicles along the route.

It is an object of this invention to communicate with vehicles in anovel and effective manner.

It is another object to signal the operator of the vehicle in a noveland effective manner so as to give him more information than he couldobtain by other previously employed signalling sys- Another object is toprovide means for keeping the operator of a vehicle in continuouscontact with the dispatcher of the vehicle.

Another object is to communicate between two or more vehicles operating-along a fixed route.

Another object is to provide a continuous multi-channel telephone,telegraph and/or facsimile communication with a plurality of vehiclesalong a xed route.

Another object is to provide continuous communication for trains andother vehicles along a fixed route which is uneected by tunnels,bridges, or the like.

Another object is to provide one or more telephone channels forvehicles, such as railroad train Pullman cars.

Another object is to indicate continuously, instantaneously, andsimultaneously the location of vehicles along a fixed route at a fixedstation or stations, or in one or more of the vehicles, or both.

Another object is to indicate the speed and direction of -one or morevehicles along a fixed route at a terminal or in the vehicles, or both.

Another object is to provide a low-power consuming system for carryingout the above objects.

Still other objects will appear from time to time in the descriptionwhich follows.

The communicating system of this invention adapted for vehiclesfollowing a fixed route comprises the following essential elements: (l)a terminal radio transmitter and receiver: (2) a line or cable forcarrying video and higher frequency signals from the terminal along theroute;

(3) decouplers, which may include repeaters and/or radiotransmitter-receivers, located at spaced intervals along the cable forconnecting the cable with radiating means, such as radiatingtransmission lines, which parallel separate sections of the route; and(4) a radio transmitterreceiver on each vehicle, having an antennaradiation coupled with the nearest radiating means on the cable alongthe route.

This communicating system is adapted for the transmission and receptionof operational, safety, and general communication signals to, from. andbetween vehicles, including the communication of one or more facsimilechannels, a plurality of telegraph channels, a plurality of telephonechannels, and a channel for indicating the location, direction and/orspeed of each vehicle, such as by quasi-radar or other means hereafterdescribed. The vehicles may be of any type which can pass along a fixedroute, such as an automobile, a bus, a truck, a railroad train, anairship, or a boat.

The main radio-transmitter and receiver terminal, hereinafter referredto as the west terminal, comprises: means for modulating signal energiesof different types on a radio wave having a frequency of at least videofrequency, and transmitting this high frequency wave over the cable andradiating means along the route. This terminal also includes means forreceiving a similar modulated high frequency wave having a differentfrequency from that of the transmitted wave, including means fordemodulating the signals on the received Wave to indicate intelligencefrom the vehicles along the route or other terminal stations along theroute, as well as means for indicating the location, speed, anddirection of the vehicles along the route. For two-way communication toand from a vehicle or other terminals itis desirable to have twoseparate carrier waves of different frequencies, one for incomingsignals, and the other for outgoing signais.

Any received radio Wave may be demodulated and/or re-transmitted fromanother terminal station along the route, or at the other end of theroute hereinafter referred to as the east terminal, or if desired, itmay be transmitted from any one or more of the vehicles along the route.These other terminals along the route may be spaced any desirabledistance apart, for example 50, 100, or 200 miles.

The signals on the carrier waves are preferably modulated on pulseswhich may be amplitude, frequency, or time modulated. Time modulatedpulses are preferred in that they may be more easily transmitted withless distortion and may be easily distinguished in shape, such as width,from each other and other signal channels including location-indicatingand echo pulses and a synchronizing pulses. 'lhe time modulated s18-nal, channel pulses may be made very narrow, that is 1/2 to onemici'osecond in duration and thereby require very little energy fortheir transf mission. A preferred form of a modulated carrier wavecomprises (l) a channel of synchronizing pulses ,mterleaved with a (2)plurality of channels of signal modulated pulses, as well as (3)location-indicating pulses, wherein the three dierent classes of pulsesmay be 'readily distinguished from each other in some characteristic,such as by width. One out of every given number of synchronizing pulsesmay comprise a location-determining or radar pulse which radar pulse maybe transformed in shape or width, different from the signal,synchronizing, and radar pulses, by the vehicle receiving it, and thenbe retransmitted as a location-indicating or echo pulse.

It the interleaved trains of channel pulses are composed of highfrequency components at a video or higher frequency, (say as high asmegacycles), it is not necessary that the pulses be modulated on a radiocarrier frequency, since they then may be directly transmitted over thecable or other carrier medium and radiating means along the route. 1ftheir frequency, however, is below video frequency, it is desirable thatthe pulses be modulated on a radio frequency carrier which may have afrequency of say about 500 to 5,000 megacycles. The frequencies of thepulses on the carrier waves of the incoming and outgoing signals may ormay not be in synchronism depending upon whether the locationindicatingor echo pulses are carried at random or in a separate channel over thecarrier medium. If the echo pulses are carried at .random over thecarrier medium they may interfere with one or more of the signalchannels, producing an audio hum after the signal channel pulses havebeen demodulated. However, this hum may readily be filtered from theaudio signal without materially effecting its intelligence.

The location indicating device coupled with the receiver in the westterminal may comprise (1) a quasi-radar indicating device, such as acathode ray tube having fluorescent screen, or (2) it may comprise apanel having lights or the like corresponding to each different sectionalong the route. 1n the quasi-radar system, the sweep circuit of thecathode ray tube may be so synchronized and the uorescent screen of thetube may be so calibrated, that one sweep of the beam across or aroundthe screen corresponds in time to the length of the route or sectionthereof, such as between it and the next terminal along the route. Thevehicles may produce bright dots along the calibrations of the screencorresponding to and located along the route. The speed and thedirection of the vehicle along the route may be indicated by timing themotion of the dot over the screen of the cathode ray tube. In the otherlocation indicating system the route may be divided into sections orblocks, each of which may produce an identifying signal, such as byreshaping a radar or other location-determining pulse transmitted fromthe vehicle.y This identifying signal may then be selected to indicate,such as by a light on a panel at the terminal, that section or block inwhich fthe vehicle is located. If desired, the bright spot on thecathode ray screen or the light on the panel may flicker according to agiven code to identify and distinguish one vehicle from another alongthe route. These received location-indicating and echo pulses at, themain terminal may be again transmitted over the outgoing transmissionmedium to operate similar indicating devices at the other stationsand/or in the vehicles along the route. In view of the retentivity ofthe fluorescent screen and/or in view of the persistance ol human visionthe recurrence frequency of the radar and location-indicating pulses ofthis system may be much lower than the audio, telegraphic, or facsimilechannel pulses on these waves.

In order to keep in constant contact with the operator of the vehicleand the dispatchers at the main or west terminal, it is desirable thatat least one signal channel be continuously coupled from the westterminal to all of the vehicles along the route. Over this channeloperationalv instructions, warning signals, and the like, may beconveyed instantaneously by the dispatchers to all the vehicles. Thischannel may also be used to notify the vehicles what channels areavailable over which they may send messages to the terminal forconnection to outside communication facilities or to communicate withanother one or more of the vehicles along the same route.Correspondingly, separate signal channels should be provided for eachvehicle along the route so that the operator in the vehicle may be incontinuous contact with the dispatcher at the terminal. f

The line or cable from the terminal along the route should be capable ofcarrying waves of video and high frequencies including radio frequencywaves with as little loss of energy by radiation or other means aspossible. Such a line or cable may be shielded such as a coaxial cable.In order to reduce the power required at the terminal transmitter theremay be placed along the cable a plurality of simple low power repeatersfor amplifying the channel pulses. There may be provided separate cablesfor the two different carrier frequencies, or a single cable may beprovided whereln the repeater separates the two carrier frequency wavesand separately amplifies them in their respective directions of travel.These repeaters may be powered from independent energy sources, such asan electric line specifically for that purpose, any local power line,electricity carried in the cable itself, storage batteries, or the like.

At spaced intervals along the route decouplers are provided for couplingthe cable to a radiating means such as a radiating transmission linewhich extends along the route, within about 10 or 2O feet of the path ofthe vehicles, for radiating the energy to the vehicles. Separateradiating means may be provided for each of the two carrier frequenciestransmitted over the cable. However, one radiating means may be used ifit is blocked from transmitting when receiving, and vice versa. Theradiating means preferably extend along the route from one decoupler tothe next adjacent decoupler along the route. The decouplers may alsoinclude a repeater and/or a radio frequency transmitter and receiver oflow power, say one or two watts. Furthermore, the decoupler may comprisemeans for identifying its position or its block along the route. 'Ihepower for operating the decouplers may be supplied by any one of themeans previously mentioned for operating the repeaters.

Each vehicle is provided with a transmitter and receiver similar to thatprovided at the terminals and may also include an indicating device ofthe type previously described. The radio transmitter-receiver on thevehicle is radio-coupled to the nearest radiating means along the routethrough a suitable antenna or lloop for gathering the radiated energyfrom the radiating means. It is desirable that separate antennas beprovided for the separate radiating means, one for each carrierfrequency. The vehicle transmitting equipment operating at the outgoingfrequency may also be coupled to receive synchronizing pulses so thatthe signal channels to be transmitted from the vehicle may be insertedin the proper channels of the outgoing frequency wave.

The transmitter and receiver circuits on the vehicle also includemodulating and demodulating circuits, location pulse selecting circuits,synchronizing pulse selection circuits, and means for reshaping theradar pulses into location-indicating or echo pulses for retransmissionon the outgoing frequency. A suitable cam flicker arrangement may beinserted in the location-indicating pulse forming a circuit to identifyeach vehicle. If a. separate channel is provided for location-indieatingpulses the reshaped radar pulses may be blocked except when this channelis in synchronism with these reshaped pulses. In such a system therecurrence rate channel pulses in the two carrier waves is slightlydifferent so that the lccation-indication channel will pass all of thechannel positions on the other wave a sumcient number of times eachsecond so as to transmit suillcient echo pulses to provide anintelligible signal at the terminal location-indicating device.

The communication system of this invention may be adapted for one ormore fixed parallel routes, or separate systems may be installed foreach route. It is immaterial whether or not the route carries vehiclestravelling in the same or opposite directions.

These and other objects and features of the invention will become moreapparent upon consideration of the following detailed description to beread in connection with the accompanying drawings in which:

Fig. 1 is a schematic diagram of portions of the system of thisinvention adapted for use along the railroad track;

Fig. 2 is a schematic block diagram of a repeater used in the singlecoaxial cable system shown in Fig. 1;

Fig. 3 is a schematic block wiring diagram of a decoupler coupled to thecoaxial cable shown in Fig. 1;

Fig. 4 is a schematic block wiring diagram of the main or west terminalcircuit shown in Fig. 1;

Fig. 5 is a graph of wave forms useful in explaining the operation ofthe system shown in Fig. 4;

Fig. 6` is a marker pulse generator and selector circuit diagramemployed in the system of Fig. 4;

Figs. 7 and 8 are graphs of wave forms instrumental in explaining theoperation of Fig. 6;

Fig. 9 is a schematic wiring diagram of a pulse width selector circuitemployed in the circuits of Figs. 4, 11,'12 and 16;

Fig. 10 is a graph of wave forms useful in explaining the operation ofthe circuit in Fig. 9;

Fig. l1 is a, schematic wiring diagram of a transmitter-receiver circuitemployed in the vehicle, such as the train shown in Fig. 1;

Fig. 12 is a schematic wiring diagram of the East terminal circuit shownin Fig. 1;

Fig. 13 is a graph of wave forms instrumental in explaining a modifiedoperation ofthe circuits shown in Figs. 4, 11 and 12;

Fig. 14 is a lblock wiring diagram of a, cable decoupler circuit,similar to that shown in Fig. 3, adapted for use in a modiiication ofthis invention.

Fig. 15 is a graph of wave forms useful in explaining the operation ofthe circuit of Fig. 14;

Fig. 16 is a block wiring diagram of a west terminal circuit adapted foruse with the modiilcation shown in Fig. 14;

Fig. 17 is a. graph of wave forms useful in explaining the operation ofthe modification shown in Fig- 16:

Fig.v 18 is a graph of wave forms useful in explaining the operation ofthe circuit shown in Fig. 9 according to the modification shown in Fig.16;

Fig. 19 is a block wiring diagram of a receiver and transmitter circuitfor a vehicle such as the train with the modication shown in Fig. 16;and

Fig. 20 is a block wiring diagram of an east terminal circuit for themodiiication shown in Fig. 16.

For the purpose of illustration and simplicity, the system of thisinvention will be described as adapted for use in a communication systemfor railroad trains. This description will be divided into two majorsections, the rst of which has two modiications:

Chapter IA dealing with a quasi-radar pulse location and communicationsystem wherein the radar pulses may appear in any position over thecarrier medium and may interfere with signal channels (illustrated inFigs. 1-12);

Chapter IB dealing with a quasi-radar pulse location and communicationsystem wherein the radar pulses are assigned a definite channel on thecarrier medium and do not interfere with other signal channels(illustrated in Figures 4, 11, 12, and 13); and

Chapter l1 dealing with a system for signal communication and locationof trains in different blocks or sections along the route (illustratedin Figs. 14-21).

CHAPTER IA (1) Tm: Lnm Cmcmrs Referring to Fig. 1 there isdiagrammatically shown a west terminal I, which will be considered amain terminal, and an east terminal 2 connected by a. single coaxialcable 3 along a railroad right-of-way 4 upon which is shown a train 5.At spaced intervals along the cable 3 there is shown a repeater circuit8, a decoupler circuit l, and a, combination decoupler and repeatercircuit 8. From the west terminal l and from each of the decouplers 1and 8 there is shown a pair of radiating transmission lines 9 and I0which extend along each section or block of the track B to form a radiocoupling with the antennas or loops II and I2, respecti'vely, on thetrain 5.

The radiating transmission lines 9 and I0 may comprise a pair of spacedparallel conductors which terminate in a high impedance I3. The spacingshould be maintained as constant as possible to avoid energy loss,particularly if the wires are closer together than about 6. inches. Theradiating transmission lines 9 and I0 should extend the complete lengthof each section along the track and should not be more than about 20feet away from the antennas on the trains at all times and the closerthe better. They may be supported on line poles along the track or 'lother means. The two pairs of radiating lines may both be locatedvertically one above the other on the same side of the track or one eachside of the track as desired. The train, meaning the locomoia've or anyone or more cars in the train, should carry the antennas ii and I2, asclose as possible to their corresponding radiating means 3 and l0 butthey may be located on top, or on either or both sid of thetrain. Byusing the close spacing relatively low power may be` used, so thatradiation iields are ineiective at distances from the track.

The repeater circuit i which may be placed at intervals along the singlecable 3 to maintain a strong Signal the full length of the route maycomprise a two-way iilter ampliiier circuit as shown in Fig. 2. Thefrequency of the carrier wave .from terminal I will be hereinafterreferred to as il and the frequency of the carrier wave from terminal 2will be referred to as f2. the fl carrier wave in the cable 3 from thewest terminal passes through line I4 to the f1 dlter I5 wherein it isselected from the f2 frequency in cable 3. The separated f1 carrier thenpasses through line Ii to a suitable amplifier I1, preferably of aboutone watt or less, which may be supplied with power from any suitablesource along the railroad or through the cable 3. 'I'he ampliiier i1passes the amplified ji wave through line i8 into cable 3 again forfurther transmission. The ,i2 carrier wave :from the east terminal inline 3 is withdrawn through line i9 into the y2 lter 2l wherein it isseparated from the f1 wave and then ampliiied in ampliiier 2l, similarto i1, for further transmission through line 22 to the cable 3. Theimpedance of iilter i5 and amplilier 2i should be matched with that ofthe cable 3 entering these two circuits toward the west. and similarlythe impedances oi' ampliiier l1 and iilter 2l should be matched with theimpedance of the cable 3 toward the east. Ii desired, separate matchingimpedances may Ibe inserted at the ends of the cables 3 which are joinedto lines I4 and 22, and I8 and I9, respectively.

Ii.' separate cables are used for the two directions of transmission therepeater circuits need only comprise ampliilers, since no separation ofthe waves is necessary.

The decoupler 1, also coupled to the cable 3, may comprise a circuitsimilar to that shown in Fig. 3 wherein the carrier wave f1 from thewest is passed from cable 3 through the lter 23 for separating wave f1from wave iz. The separated wave f1 may then be passed directly into thedecoupler 24, and if the frequency of wave f1 is suiiiciently high andof suihcient strength it may be passed directly through line 25 into theradiating means 9. However, if the frequency is too low to radiate, itshould be passed through a suitable radio frequency transmitter 2S formodulation on a radio frequency wave which is then radiated in theradiating means 9 extending along the track 4.

Similarly, the carrier wave f2 in cable 3 from the east is separated inthe filter 21, and may be directly passed to the decoupler 28. Then, theseparated wave is passed through line 29 into a marker pulse selector 3Qwhich separates the synchronizing or marker pulses from the signalmodulated pulses on the wave from the east terminal 2. These separatedmarker pulses then are passed to a transmitter 3| for transmission at asuitable radio frequency over the radiated transmission line lil, ifthey are not of suiilciently high frequency .for direct transmissionfrom the line Thus,I

8 Il. The reason for transmitting these marker pulses is to synchronizethe transmitter on the train so that the signals from the train may beproperly interleaved in the available channels on the carrier wave f2.

Also, connected to the radiating means I0 is a receiver 32 of anysuitable design, which may, if the frequency of the received signal issuliiciently high, be only a coupler for coupling the received impulsesfrom the antenna, I0 to the cable 3 through line 33. However, if thereceived impulses are not modulated on a wave of frequency f2, they maybe detected and remodulated in a suitable radio receiver circuit, whichmay be `a crystal type detector and may even be a superheterodynecircuit.

To prevent the transmitted selected pulses from (2) THE WEST AND MAINTERMINAL CIRCUIT (a) The train circuits Referring now to the west mainterminal circuit schematically shown in Fig. 4, the base wave generator36 may comprise a, sine wave generator having a frequency of, say about10,000 cycles, which base sine wave is then passed through line 31 to amarker and radar pulse forming circuit 38 and a. signal modulatingcircuit 39, from which circuits is produced a complex multichannel pulsewave 40 shown in Fig. 5. On this wave 40 are shown: a marker pulsechannel wM which may comprise a pair of closely spaced pulses oi.' shortduration; a plurality of time modulated signal channel pulses w1, wz,w3, wn; a location or radar pulse we which takes the place of one markerpulse wM but may have a frequency much lower than that of the markerpulses, that is, one in out of every 25 marker pulses may be a. radarpulse; vehicle or train location pulses t' and t"; and may also have thenext or east terminal location pulse Te.

The'marker and radar pulse forming circuit 3l produces the pulses wM andwa as follows: The sine wave from generator 36 is passed into the pulsegenerator 4| in which is produced a pulse wave having a frequency of,say, 10000 cycles. This pulse wave is then passed into a marker pulsegenerator 42 as Well as a Wide pulse generator 43. 'Ihe marker pulsegenerator 42 may comprise a circuit similar to that shown in Fig. 6 forproducing from the pulse wave 44, shown in Fig. 7, a pair of pulses toform the marker pulse wave 45, shown in Fig. '7.

Tracing the pulse wave 41 through the circuitv in Fig. 6, it is passedthrough line 46 into a suitable decoupler and ampliiier tube 41 from theplate of which tube is withdrawn a pulse wave similar to wave 44. Thiswave 44 is passed into the open-ended delay line 48 comprising a networkof inductances and condensers 49 and 50, respectively, which delays thewave 44 an amount t as shown in Fig. 7. The closed end of the delay line48 is bridged with a balanced impedance 5| to prevent furtherreflections of the pulse wave.-

The open-end 52a of the network 48 prevents inversion of the pulsesreflestej therefrom. The reilected delayed pulse wave and the originalpulse wave from the plate of tube 41 are then mixed to produce thedouble marker pulses on wave 45 which is withdrawn through line 52 Thisdouble marker pulse wave 45 is then passed into gate circuit 53, shownin Fig. 4, which is normally maintained open for passage of the markerpulses through line 54 to the mixer 55, referred to later. l

The wide pulse generator 43 may comprise a suitable multivibrator orsimilar trigger circuit for producing the pulses wa which must be atleast as wide as the outside edges of the pair oi marker pulses wmproduced in the circuit 42. These marker pulses um are passed throughline 56 into gate circuit 51 which is normally closed, except for onetime out of every 25 consecutive the marker pulses wn, at which time thegate 53 is closed and the wate 51 is opened for the insertion of thepulse um in place of that marker pulse um.

The control oi' the gate circuits 53 and 51 may be accomplished bydividing the sine base wave from generator 36 in the frequency divider58 to produce a wave having 400 cycles which is then passed through line59 to the blocking pulse generator 60 which then controls the gates 53and 51 through lines 6I and 62 as previously described. Thus, every 25thmarker pulse may be a wider radar pulse wa which is passed through line54 into the mixer 55.

The signal modulating circuit 39 may comprise a suitable delay device-63 for delaying the sine wave from generator 38, diiierent amounts toproduce a series of delayed sine waves out of phase with each other andmarker pulses wir. The resulting delayed sine waves may then bemodulated in a suitable modulator 64 according to signals w1, wz, w3 wnintroducing into the modulators over lines 65 and 66, etc., from aswitchboard 61.

The details of the various devices indicated by block symbols, in theseveral circuits, may take the forms disclosed more iully in Reeves andBeatty patents, Nos. 2,266,401 and 2,300,394 respectively. The timemodulated pulse trains from modulators 64 are passed into the mixer 55from which is withdrawn the resulting modulated multichannel pulse wave40 through line Gvto a suitable decoupler or f1 transmitter 69 coupledto a radiating transmission line 9 and to the coaxial cable 3 throughline 10.

Signals w1, wz wn which may be transmitted over the Wave 40 may comprisea single channel for signaling the operator of each train, which channelis continuously and simultaneously connected to all of the trains andover which channel the dispatcher at the main terminal I may control themovement of the trains, either through the engineer or the conductor, orautomatically. 'I'his signal channel may be an audio, a telegraphic ora, facsimile channel, or separate chanels may be provided for each ofthese types of communication to the operators oi the trains. Sincetelegraphic channels do not require as wide a frequency band as audiochannels, one audio or telephone channel may be divided into severaltelegraphic channels. The other audio signals channels may be connectedto separate telephones in each train, such as telephone in Pullman carsfor use of passengers.

(b) The receiver circuits The receiver portion of the west terminalcircuit is also coupled with the coaxial cable 3, and may comprise asignal modulator circuit 1| and a. location indicating circuit 12. Thereceived carrier wave .f3 on which is modulated signals from the trainsand the east terminal 2 may be graphically represented as wave 13 inFig. 5. This wave is passed from line 3 through line 14 or is receiveddirectly over the radiating transmission line i0, both connected to asuitable f2 receiver 15. This receiver may comprise an f2 iilter anddecoupler circuit, and/or a radio detecter for the carrier wave fr. Thereceived wave 13 is then passed into the marker pulse selector 16 toremove the double marker pulses em shown thereon for syn chronizing thedemodulator circuit 1I.

The marker pulse selector circuit may comprise the decoupler amplifier41 and reiiecting delay line network 48 previously described in Fig. 6,plusk a mixer-clipper 11. In this circuit the received wave 13 shown inFig. 8 is mixed with the same wave delayed suilciently to cause theiirst one of a pair of the marker pulses eM to be super-imposed upon thesecond one oi' a pair of the marker pulses to produce a double amplitudepulse 18 as shown on wave 19, in Fig. 8. The double amplitude markerpulse 18 ls then clipped above the level 80 in the mixerclipper 11 toproduce a pulse train 8|' which may then be passed through line 82 intoa blocking wave generator 83 for synchronizing the demodulator circuit1|.

A suitable demodulator circuit may comprise a delay device 84 forproducing a series oi delayed blocking waves for separating each of thesignal channels on the wave 13. These delayed blocking waves are thenmixed in the deblocking circuits 85 with the original Wave 13 coupledthrough line 86 for separating each signal channel into a train ofsignal modulated pulses. These separated trains are then passed into theseparate demodulator circuits 81 to reproduce the audio or other signalsmodulated` thereon.

The resulting modulated signals may then be passed through hum filters88 to remove the hum caused by the interference of the wider locationindicating or echo pulses t', t", TE, etc., on the wave 13. Since therecurrence of these echo pulses occurs only 400 times a second, thefilters 88 may be constructed to remove only the vibrations of 400cycles and its harmonics, namely, 800, 1200, 1600, etc., cycles. Thesharp removal of vibrations at these particular frequencies from thedemodulated audio signals e1, ez, en does not materially affect theirquality or interfere with their intelligence. The resulting ltered audiosignals may then be passed through lines 89 and 90 to the switchboard 61from which they may be coupled to outside telephone or signal circuitsthrough lines 9| or transmitted again through the outgoing channels 65,66, etc., to other trains or points along the railroad, such as the eastterminal.

(c) The location indicator circuit Thelocation indicator circuit 12 isdirectly coupled to cable 3 through line 92 and comprises a Widthselector circuit 93 for separating the location indicating or echopulses t', t", Ts, etc., from the wave 13. All of these echo pulses havebeen made wider than the signal modulated pulses e1, ez en or either oneof the pair of marker pulses eM, and the width of these echo pulses isone less than the distance between the pair of marker pulses eM. Thus,these echo pulses will not interfere with or be selected by the markerpulse selector 18.

The width selector circuit 93 may comprise a circuit similar to thatshown in Fig. 9. The posivenience in the graph in Fig. 10, is introducedat |06 into the ampliier tube |01. From the plate ot amplifier tube |01the wave 13 is passed through resistance |08 into the time constantcircuit |09 comprising a variable condenser ||0 and inductance Ill. Thistime constant circuit |09 is tuned to frequency corresponding in time totwice the width of the narrowest width pulse to be selected. Forexample, the excitation of the circuit |09 by the leading positive edgeof pulse t' causes an undulation on wave ||3 (shown in Fig. 10) to beproduced from circuit |09. The trailing edge of pulse t' correspondsexactly to the center zero position of this undulation so that thepositive undulation ||2 is not counteracted but is aided by any changein potential of the trailing edge of pulse t' on wave 13. The next pulseH4 in wave 13, which is narrower than pulse t', produces a much smallerun-v dulation ||5 on the wave H3, since shortly after the circuit |09 isexcited by the positive leading edge of pulse ||4 it is counteracted bythe trailing edge of the same pulse, thus preventing the positiveundulation ||5 from reaching as high a potential as the undulation ofpulse H2.

To prevent the circuit |09 from continuing its oscillations there isinserted a damping tube ||6 from the cathode of which is withdrawn thewave ||3 above referred to. This wave then passes into a suitableclipper circuit comprising a clipper tube ||1 having a variable bias I|8for adjusting the clipping level ||9 (shown in Fig. 10) vto a valuewhich will clip the undulations formed from the pulses to be selectedand eliminate the others. The resulting output from the plate of tube||1 is illustrated by wave |20 which is withdrawn through line |2l. Thepulse wave may be suitably shaped in a circuit not shown, before beingpassed through line 94a (shown in Fig. 4) and also 94, if desired.

Instead of the width selector circuit shown in Fig. 9 the marker pulseselector circuit shown in Fig. 6 may be employed for selecting pulsesgreater than a given width by delaying the train of pulses an amount intime equal to the widest pulse not to be selected, and thensuper-imposing the delayed pulse train on the original undelayed pulsetrain and clipping ofi the overlapping portions in a suitablemixer-clipper, such as 11. This operation of selector in Fig. 6 as awidth selector will be further described in connection with a markerpulse selector |26 shown in Fig. l1 and the pulse |21 shown in Fig. 8.

The resulting separated location or echo pulses t', t, TE, etc., arethen passed through line 94 to the grid 95 of the cathode ray tube 96.This cathode ray tube is also provided with a rotating sweep circuit 91synchronized by the original radar pulses we formed from the frequencydivider 58, through line 98. The electron beam produced in the gun 99 ofthe tube 96 may be caused to be deected around the circle |00 shown onthe screen |0I. Every time a width pulse is passed through the widthselector` 93 the biased grid 95 c auses the beam to produce a brightspot of light on the path |00. A scale may be placed over the screen |0|to measure the distance between the starting point Tw or |02,corresponding to this west terminal and the bright spot |03corresponding to the location of the east terminal caused by pulse Tn.This distance around the path |00 between |02 and |03 may be calibratedinto separate blocks. miles tion or echo pulses from-each of the trainsalong the track 4 will then produce bright spots |64 and |05 caused bypulses t' and t". Thus, the distance of these trains from either or bothterminalsis immediately and continuously indicated on the screen |0I,and the speed and direction at which these dots move along the scale isdirectly proportional to the speed and direction of the trains along the.track 4. If desired, the radar pulses wn may be passed from line 64toline 92 through a line 92a to produce a bright spot Tw at |02 on thescale |0|.

The received location pulses t', t", Ts, Tw. etc., removed from thepulse wave 13 in theselector 93 may also be transmitted over wave 43 byconnecting the selector 93 tov the mixer 55 through line 94a. Thisproduces the randomly placed pulses t'. t", Ts. etc. on the wave 4 0.

(3) THE TRAIN CIRCUITS In Fig. 11 is shown a schematic diagram of-thereceiver and transmitter circuits which may be employed in the train 5,operating along the track 4 shown in Fig. 1. This circuit comprises areceiver antenna which is coupled to an fr receiver |22 for receivingthe complex pulse wave 40 transmitted from the west terminal This pulsewave 40 is passed into two separate circuits: a signal demodulatingcircuit |23 and the location indicating circuit |24.

(a) The receiver circuits The received pulse vtrain 40 is passed fromreceiver |22 through line |25 to a marker pulse selector |26 whichselects pulses wir and ws from the wave 40. This marker pulse selectormay be similar to the selector shown in Fig. 6. The radar pulsey we, onwave 40 is selected similarly to the pulse wir, as is shown in Fig. 8.because the width of the pulse um. is at least as wide as the outsideedges 'of the pair of pulses wu. Thus, at least a portion of the pulsewn delayed in the network 48 of Fig. 6 will overlap a portion of theoriginal pulse wn to produce the increased amplitude pulse |21 whichwill be clipped in the mixer-clipper 11 to produce' the pulse wave 8|.This pulse wave 8| is passed through line |28 into the demodulatingcircuit |23 comprising a blocking wave generator |29, similar togenerator 83 in Fig. 4. The resulting blocking wave is then passedthrough at least one xed delay device |30 for separating the wi signalchannel reserved for all and thence through line |3| to another or aselective delay device |32 which may be adjusted to select differentreceiving channels wz,

Y wa, wi, etc., as desired, by means of contacts |33 so that any one ofthese channels may be selected and deblocked from the incoming wave 40.The delayed blocking waves from the devices |30 and |32 are then passedinto the deblocking circuits |34 where they are combined with theoriginal received pulse wave 40 through line |35 to produce separatetrains of pulses corresponding to the signal channels deblocked. Theseseparated trains may be respectively passed to the demodulator circuits|36 for demodulation and thence through hum eliminators or lters |31 toremove the hum caused by an interference with the echo pulses t. t", TE,etc. These filters |31 are similar to filters 88 of Fig. 4 previouslydescribed. From these lters may be withdrawn through lines |38 thesignal Wi and one or more other of the signal channels selected by thedevice |32 to a suitable intelligence or other units, as desired. Thetransmitted locaconverting device such as a telephone, or if de- (b)Location indicator circuit 'I'he location indicator circuit |24 isSimilar to the circuit 12 shown inFig. 4 and is controlled by thelocation and Wider pulses t'. t", Ts and wr on the wave 40 which ispassed from the receiver |22 through line |39 to a width selector |40,similar to the circuit shown in Fig. 9.

Radar pulse wlis shown in Fig. on wave 40 l to be wider than pulse t',but it produces ah undulation ||2a similar to that of l2 on wave ||3having a greater amplitude than the undulations produced by the pulsesnarrower than pulse t'. Therefore pulse wr is also selected with thepulse t' and t" on the wave 40. Thus by properly controlling the gatelevel 9 and the adjustments ||0 and ||8 all pulses wider than a certainwidth may be selected, referred to as the type C in the drawings.

The resulting selected wide pulses control the grid I4| of the cathoderay tube |42 through line |43. The sweep circuit for the rotating beamfrom the electron gun ||4 of the tube |42 is controlled by the plates|45 through a sweep circuit |46. This sweep circuit |46 in turn iscontrolled by the wide radar pulses wlwhich may be selected from thewidth pulses from selector |40 by the mixer-clipper |41 coupled to themarker pulse selector |26 through line |48. The combination of themarker selector pulses from selectors |40 and |48 produces a pulse ofincreased amplitude corresponding to pulses wr which are clipped oi inmixer clipper |41 and then may be passed through a suitable shaper |49before being passed through line |58 to control the sweep circuit |46.Thus, the locations of both the east and West terminals as well as thetrains along the track are shown as bright spots on the screen |5| ofthe tube |42.

Before the selected radar pulse wlis transmitted from the train as alocation indicating or echo pulse t', it may be reshaped, such as tonarrow it say to about V2 the width of the pair of marker pulses, in asuitable multivibrator circuit |53 to prevent its selection as a markerpulse on the outgoing fz carrier wave. The reshaped and new echo pulset1 is then passed through line |55 to the transmitter through the mixer|56.

(c) The transmitter circuits) The receiver |58 for synchronizing thetransmitter |51 on the train are both coupled to the antenna I2. The f2receiver |58 only receives at least a. portion of the marker pulses eMof wave 13 (as previously described in Fig. 3) to trigger the base Wavegenerator |59 for synchronizing the transmitted pulses e1, e2, es en.The base wave from generator |59 is passed into delay device |60 andthen may be passed into an afliustable delay device |6I, adjustablesimilar to the device |32 above mentioned. From these delay devicesdelayed waves are produced to control the signal modulator circuits |62from which are withdrawn trains of pulse modulated signals correspondingto channels e1 and e4 which may be reserved for this railroad train. Thesignals el,

it e4 ea to be modulated may be connected to a switchboard on the train(not shown). The resulting trains of signal modulated pulses are thenpassed to the mixer |58 to form wave 13 which is then transmitted overantenna I2 by the fz transmitter |51.

In order to prevent the transmitted signals from transmitter |51 frompassing back into the receiver |58 the receiver |58 is blocked throughline |63 when the transmitter |68 is transmitting.

(4) Tm: vEAST on OTHER TERMINAL Cmcnrrs (a) The receiver circuit Acircuit for the eastterminal 2 "shown in Fig. 1 is schematicallydisclosed in Fig. 12 wherein the fr receiver |65 is coupled to the cable3 and receives the multichannel pulse train 40. This receiver may besimilar to those previously men tioned coupled to the line 3, and maycomprise a signal demodulating circuit |66 and a location indicatorcircuit |61, similar to that previously described on the train in Fig.11.

From the receiver |65 the wave 40 is passed through a marker pulseselector |68, similar to selector |26 in Fig. 1l, and thence into thecircuit |66 comprising a blocking wave generator |69 and a. delay device|10 from which is withdrawn a plurality of delayed waves correspondingto each of the signal channels on the wave 40. These delayed Waves areseparately connected to suitable deblocking circuits |1| to separate thechannels from the wave 40 which is also coupled to circuits |11 throughthe line |12. These resulting separated pulse trains may then beseparately demodulated in suitable demodulation circuits |13 and thencepassed through lters |14, similar to lters 88 and |31 previouslydescribed, and from which they may be connected to a switchboard |15.

The location indicator circuit |61 may comprise a type C Width selector|16, similar to selector |40, for selecting from the wave 40 introducedinto line 11 all those pulses having a width equal to or greater thanthat of the location pulses t', t", TE, etc. These pulses are thenpassed from the selector |16 through line |18 to the grid |19 of cathoderay tube |80 to control the electron beam from the electron gun |8| andto produce the spots on the target |82 of the tube |80. The rotary sweepcircuit for the electron beam is controlled by pulse wa selected fromthe wave from selector C in the mixer-clipper |83 as previouslydescribed in Fig. 11. A shaper |84 may be inserted before the selectedwa pulses trigger the sweep circuit |85 connected to the deflectionplate |86 in the tube 80. The shaper |84, may also narrow the selectedpulse um so that it may have the same width as pulses t and t", toproduce pulse Tr: which is then passed through line |81, througli'aslight delay device |88, and thence to mixer |89 and fr transmitter |90of the transmitter circuit for the east terminal.

The transmitter circuits board |61 of tne west terminal circuit channelsfrom the west terminal, as well as outside channels through lines |16,may be connected to the signal channels e1, ez en. The resulting signalmodulated pulses from modulators |92 are then mixed in the mixer |89 andthe resulting complex pulse wave 13 is passed into the f2 transmitter|90 and thence back into the coaxial cable, through line |94.

The marker pulse en on wave 13 may be in synchronism and made directlyfrom the marker pulses wir selected in circuit |69. These selectedpulses Vum may be passed thru line |95 to a new marker pulse generator|95a and the resulting marker :pulses may be then passed through line|95b into the mixer |89 and thence to transmitter |90. The delay device|88 is inserted in the line |89 to delay the echo pulse Tr: so that itwill not superimpose or interfere with the marker pulses eM on the wave13, thus produced in synchronism with pulses wm.

As shown in Fig. 5, the location or echo pulses t', t", and Tw occuralong the pulse waves at random and may be even superimposed on one ormore of the signal modulated channel pulses. However, such interferenceis, comparatively speaking, so rare that a loss of either or both of theinterferring pulses cannot be readily detected after sound demodulationor projection on a rententive fluorescent screen of the cathode rayindicating device.

CHAPTERIB Instead of producing waves as shown in Fig. wherein the echoand location indicating -pulses occur at random over the transmissionmedium and may superimpose themselves on certain of the signal channelpulses, the circuit in Figs. 4, 11 and 12 may be modified to producewaves similar to those shown in Fig. 13 wherein a separate channel orspace is reserved after each marker pulse pair for the insertion of thewide location indicating and echo pulses. This is accomplished by havingthe frequency of channel pulses on the fr wave from the west terminalslightly different from the frequency of the channels on the f1 wavefrom the east terminal, and providing means for-'blocking the lines fortransmitting the echo pulses except when the spaces reserved for themoccurs. `These changes may be accomplished by throwing the switches ineach of the above mentioned Figs. 4, l1, and 12, which may be ganged orconnected to the arms shown in heavy dotted lines.

Tracing this modification through the circuit in Fig. 4 the switch |91in line 94a is opened and the switch |98 is closed so that the train ofpulses from the width selector 93 must pass through the unblocking gatecircuit |99 before being passed into the line 94a and to the mixer 55.This unblocking gate circuit may be controlled by a multivibrator 200which is connected to the marker pulse generator 42 through line 20| andswitch 202, which switch is now closed. The multivibrator 200 may beadjusted so as to be in synchronism with the rst one or more signalchannels occurring after each marker pulse on the wave 40 reserved forthe pulses selected in selector 93. This is accomplished by unblockingthe gate |99 during the time interval of the spaces reserved thereforcontrolled by the THE WEST TERMINAL CIRCUIT 16 multivibrator 200. Thetime delay devices 63 and 84 are adjusted so that the signal modulatedpulses occur at other than the spaces reserved for the locationindicating pulses.

It is desirable that'the frequencies of the pulses and particularly themarker pulses, on the wave 203 from the west terminal on the wave and2|4 from the east terminal are sufliciently different so that the spacesfor the location pulses on each wave will pass all the positions on theother wave at least 20 or 30 times each second so that a sufficientnumber of the echo pulses will be transmitted each second to produce anapparently continuously visual indication on the cathode ray tubescreens of the location indicator devices. Since the echo pulses now alloccur only in given channel along each pulse wave, the hum filters 88are not required and thus may be shunted out by operation of theswitches 205 coupled to the other mentioned switches by the heavy dottedlines 206.

(2) Tm.' TRAIN Cmcurr (3) THE EAsr TERMINAL CIRcUrr The east terminalcircuit shown in Fig. 12, necessitates more modication than that of thepreviously described circuits in that it must produce a new base sinewave and.. frequency of marker pulses for the transmissioniof the signalpulses along the wave 204. This wave must contain marker pulses whichare out of synchronism with the marker pulses of wave 203 produced fromgenerator 36 shown in Fig. 4. This separate and new base sine wavegenerator is shown at 2|4 in Fig. 12 and may have a frequency say of11,000 cycles which is 1,000 cycles greater than that of the generator36. Such a di'erence in frequency will allow at least 30 of each of thedifferent location pulse channel spaces to pass each portion` on theother wave each second. The wave from generator 2|4 may be coupled to apulse generator 2|5 and then into a marker pulse generator 2|6, similarto that shown in Fig. 6, to produce a train of pairs of marker pulsesthat is connected to the mixer |89 through line 2| 1 by closing theswitch 2| 8.

The modulators |92 should be controlled by delayed waves from thegenerator 2|4, which waves may be produced in the delay device 2|9 andpassed through lines 220 to the modulators |92. The unblocking gate 22|in line |81 prevents the east terminal location vpulse ET from beingcontinuously transmitted to the mixer |89. This gate 22| may becontrolled by a multivibrator 222 coupled to the marker pulse generator2|6 through line 223. The insertion of the above described circuits byoperating the switch gauging means 224 disconnects the filters |16 byoperating the switching means 225, disconnects lines |9| and |95, anddisconnects the short delay device |88 by closing switch 226.

One advantage of the modiication just described resides in the fact thathum lters 88, |31 and |14 are not required in the audio circuits of eachof the demodulator circuits.

CHAPTER II (1) THE LINE CIRCUITS Instead of indicating the exactlocation oi' each train along track 4 there may be provided separatesignal means in each decoupler circuit 1 or 8 for producing anidentifying signal when a train transmits location indicating pulses tothe radiating means of that particular `decoupler corresponding to agiven block or section of track. A decoupler circuit for providing suchidentifying signals is yshown in Fig. 14 wherein two different frequencywaves are separated and transmitted and received on the antennas 9 and|0. This decoupler may comprise illters 221, decouplers 228, transmitter229 for the wave from the west terminal; and for the wave from the eastterminal, marker pulse selector 230 (similar to 30 in Fig. 3),transmitter 23| (similar to 3| in Fig. 3) for the transmission of themarker pulses to the antenna `|0, and receiver 232, blocked through line23|a when the transmitter is transmitting, for receiving the signalsfrom the train. The pulses received from the train may b e graphicallyshown in Fig. as wave 233, comprising a location indicating pulse 234,which may or may not correspond to one oi' the marker pulses on the wavefrom the west terminal, and the signal channel pulses e1, ez, etc. Thepulse 234 may be selected in the width selector 235 (similar to thatshown in Fig. 9) to produce the wave 236 which may be passed into ashaper 231 which may comprise a multivibrator for widening or narrowingthe pulse to a given width W3 shown on wave 238. This width W3 maycorrespond to that particular block decoupler circuit and when it istransmitted in place of the pulse 234 on the wave 233 it identifies theblock in which the train is located. W3 may be inserted for pulse 234 bycombining waves 233 and 238 to produce pulse wave 239, and clipping thewave 239 above the clipping level 240 in a mixer-clipper 24| to transmitonly that portion' of the wave below level 240 forming pulse wave 242Withdrawn from clipper 24| through line 243 and passed into cable 3.

A block wiring diagram of the west terminal circuit employed in thissystem of block location indicators is shown in Fig. 16 wherein the basesine wave generator 244 (similar to 36 in Fig. 4) controls the marker(and, if desired, also a radar type) pulse generator and a plurality ofsignal channel modulator circuits 245 (similar to 38 in Fig. 4) toproduce a multichannel pulse wave 246, shown in Fig. 17. This wave 246may be transmitted through f1 transmitter 241 .on to the lines 9 and thecable 3.

'Ihe f2 multichannel pulse wave 243 from the east terminal received fromcable 3 or line |0 in the f2 receiver 248 may be passed through a markerpulse selector 249 (similar to that shown in Fig. 9) to a multichannelseparator and demodulator circuit 250 (similar to 1| shown in Fig. 4)provided with hum eliminator filters 25|, as previously discussed inChapter 1A.

The location indicator circuit 252 may be coupled to the receiver 248through line 253 and may comprise a group of width selectors of the typeD, which select pulses only of a given width. These width selectorcircuits 254 are then connected to suitable indicating devices such aslights 255 for indicating in whichv block a given THE WEST TERMINALCIRCUIT 18 train is located. The ilickering of the light may indicatewhich train is in that particular block.

The width selector circuit of type D is also shown in Fig. 9, but thegraph in Fig. 18 illustrates how this circuit may be employed forselecting a pulse only of a given width. In Fig. 18 there in shown aWave 251 having different width pulses W1, W2, Ws, W4. and Ws, thereonwhich may occur on the wave 243 as shown in Fig. 1'7. This wave isintroduced into the circuit at |06 and is withdrawn from the plate 256of tube |01 as wave 259 at point 258. Assume that the circuit |09 istuned for selection of pulse width Wa the curve 260 represents theoutput of circuit |09 when the circuit is tuned for selection of pulsewidth Wa illustrating the different output undulations for the differentpulse widths of curve 259. When the leading edge 26| of the pulse Ws isapplied at negative polarity circuit |09, an initial undulation 262 isproduced which is normally followed by undulations 263, 264 and so on inthe form of a damped wave. When the circuit is tuned to a frequency theperiod of which is exactly twice the width Wa the trailing edge 265occurs where the initiated oscillatory energy crosses the zero axis fromundulation 262 to undulation 263. Since the trailing edge 265 shockexcites the circuit in the same direction at this point, the undulation266 produced thereby in the circuit |09 adds algebraically to theundulation 263 to produce undulation 2,61. The next succeeding pairs oiundulations produced by the leading and trailing edges of pulse width W3would normally tend to produce a negative undulation 266 which wouldcontinue as a damped wave as indicated at 269. The damping tube ||6however eliminates the trailing oscillations so that they do notinterfere with the undulations produced by subsequent pulses applied tothe circuit |09.

A pulse width less than pulse width Wa, such for example, as pulsewidths W1 and W2 will not produce maximum undulations as great as theundulation 261 for the tuning adjustment corresponding to pulse widthWa. This is illustrated by the undulations 210 and 21| produced inresponse to the pulse widths W1 and W2. respectively. The reason forthis is readily apparent because the shock excitations produced by theleading and trailing edges of the pulses of lesser width than Wa are inpart opposed to each other as indicated by the broken lines associatedwith the undulations 210 and 21|. The undulations 212 and 213 producedin response to the greater pulse widths W4 and W5 are likewise smallerthan the undulation 26,1 since here again the oscillations produced inresponse to the leading and trailing edges of the greater pulse widthsare in part opposed to each other so that the alegbraic summationthereof is less than in the case of the undulations produced in respouseto pulse width Wa.

Y The threshold clipping stage ||1 is adjusted to clip at a level 214thereby obtaining and arnplifying the crest portion 215 of theundulation 261 as indicated by wave 216. This wave 216 then controls theoperation of the light or indicating means 255. If desired, the widthselector of the type D" employed in the system oi Fig.

16 may he provided with a peak follower clipper to select only thegreatest amplitude undulations such as 261 on wave 260 instead ofclipper ||1. Such a peak follower clipper automatically controls thelevel 214 shown in Fig. 18. Similarly pulses oi other widthscorresponding to other block decoupler circuits are selected in otherdiiIerently tuned width selectors 254 oorresponding to sections orblocks along the track 4.

(3) Tm: TRAIN CIncuIr The train circuit in this block indicating systemshown in Fig. 19, may comprise a receiver 211 coupled to the trainantenna il for receiving the pulse wave 248 from which the marker pulseseu are selected in pulse selector circuit 218. The resulting markerpulse selected wave may then be used in deblocking the received signalchannels on the wave 24| in the demodulator circuit 219.

'I'he location indicating pulse 284 shown in Fig. may be generated intwo ways, one is from a marker or radar type pulse wu or wa, and theother is from an independent pulse source. In

the first way, the marker pulse wave may ber coupled through line 280 toan unblocking gate circuit 28| which may be triggered by any random typeof a multivibrator 282 which will cause a sumcient number oi' the markerpulses to pass the gate 28| each second to control the indicatingdevices 255,shown in Fig. 16. The other way is to open the switch 280ain line 280 and produce the location. indicating pulses directly fromthe multivibrator 282 and withdraw them through line 282a. The thusproduced location indicating pulses may then be passed through asuitable shaper or trigger circuit 282 for producing the pulses 234shown in Fig. 15 which are transmitted to the fz transmitter 282 overline 284.

The train transmitter circuits may comprise suitable modulator circuits288 which are contrclled by the marker pulses onvwave 243 received inreceiver 281, as previously described in the circuit of Fig. i1.

(4) Tin: EAs'r TERMINAL Cmcurr The east terminal circuit for the blockindicating system is shown in Fig. and may comprise only a simple Ilreceiver 288, marker pulse selector 289, each of which is coupled to asuitable demodulator circuit 298 for demodulating the signal channelsreceived over wave 248. The marker pulses selected in circuit 289 may beagain transmitted with the modulated signal channels e1, ez. in the fatransmitter 29| through line 292 back to cable 3. The modulator circuits293 for channels e1, ez, es, may be synchronized with the demodulatorchannel circuits of 298 through line 294.

If desired cam flicker circuits, such as |52 shown in Fig. 11, may beinserted in lines 284 and/or 294 Ishown in Fig. 19 to indicate whichtrain is in a given block.

The above described modiilcation of a communication and block locationindicating system is similar to that disclosed in Chapter IA wherein thelocation width pulses are inserted at random on the pulse wave 243, asshown in Fig. 17. If desired, the system described in Chapter IB may beemployed in this block indicating system so that the different widthlocation pulses W1, W2,

`20 pulses, and identify the different sections or blocks along thetrack Aby a, flickering device.

If it is desired that one train alongthe track 4 wishes to talk toanother train along the same track, the modulated pulses received at theswitching terminal from the one train may be directly switched to thecorresponding terminal for transmission to the other train over theother frequency wave without being demodulated and remodulated in themodulation circuits at that terminal, after the destination of themessage has been determined at that terminal. This may be thenaccomplished by a suitable switching means operated by the switchboardoperator at the terminal.

If desired separate frequency waves may be employed for the radar andlocation pulses so that they will not interfere with the multi-channelsignal pulse waves on the circuit. However, the addition of such othercarrier waves would double the number of transmitters and receiversrequired on the train, at each terminal, and along the cable 3. Further.if desired, separate coaxial cables may be provided for each differentradio frequency carrier.

The above described system has many advantages over previously employedcommunication systems for vehicles in that it does not require aplurality of large and strong radio stations to transmit the radio wavesover long lengths of track, as well as an assigned frequency band onwhich they must operate. Also the short path radio coupling between theradiating means and the antenna on the vehicles is not affected bybridges and tunnels over and through which the vehicles may pass. If oneof the decouplers along the coaxial cable 8 becomes disabled it does notstop the whole commimication system, but only prevents reception andtransmission of signals along that portion of the track corresponding tothe disabled decoupler circuit.

While the above is a description of the principles of this invention inconnection with spelciiic apparatus and particular modiiicationsthereof, it is to be clearly understood that this description is madeonly by way of example and not as a limitation.

I claim:

l. A system for indicating the location of vehicles along a routecomprising: a transmitterreceiver terminal, a line for carrying signalsof a radiation frequency, a plurality of decouplers at spaced intervalsalong said line, each decoupler etc., will occur in a given channelreserved there- Y' for on each of the waves 242. Also, the widthlocation pulses W1, W2, W3, etc., may be transmitted over the outgoingwave 248 to the trains, so that location indicating devices, (similar to252 shown in Fig. 16), could be provided in each train as well as thatat the east terminal.

Vice versa, this block indicating system may having a radiating line, inaddition to said firstmentioned line, extending along said route betweenit and the radiating line of the next adiacent decoupler, a signaltranslator means on said vehicle having an antenna radiation coupledwith the nearest radiating means along said line. and means fortransmitting location identifying pulses at multiple megacyclefrequencies for indicating the position of said vehicle along saidroute.

2. A communication system for a vehicle following a route comprising: asingle coaxial cable extending along said route for carrying two carrierfrequency waves of video and higher frequencies, one frequency being forsignals in one direction and the other frequency being for signals inthe other direction along said cable. a plurality oftransmitter-receivers coupled to said cable at spaced intervals alongsaid route, each transmitter-receiver having a pair of radiating lines,in addition to said ilrst-mentioned line, extending along said routebetween it and the radidistinguish the trains by different widths of theIl ating lines of the next adjacent transmitter. one

asiduos y radiating means for each of said frequencies, and atransmitter-receiver on said vehicle having a pair of antennasradiation-coupled with the nearest pair oi radiating means along saidcable.

3.\A signal communication system for a vehicle following a routecomprising: a pair of coaxial cables, one carrying signals modulated atone frequency for communication in one direction, and the other carryingsignals modulated at anotherA frequency for communication in the otherdirection along said route, a plurality of decouplers coupled to each ofsaid cables at spaced intervals along said route, each decoupler havingradiating means extending along said route between it and the radiatingmeans of the nearest adjacent decoupler coupled to the same cable,signal translator means on said vehicle, and means for coupling saidsignal translator means with said cables.

4. A communication system for a vehicle following a xed routecomprising: a transmitterreceiver at one end of said route fortransmitting signals on a carrier Wave of one frequency and a radiotransmitter-receiver at a terminal at the other end of said route fortransmitting signals. on a carrier wave of another frequency, saidfrequencies being the least of video frequency, a single coaxial cableextending along said route between said terminals for carrying both ofsaid carrier waves, a plurality of decouplers at spaced intervals alongsaid route, each decoupler having a pair of radiating lines, in additionto said i'lrstmentioned line, extending along said route between it andthe next adjacent decoupler, one of said radiating lines for each ofsaid carrier waves, and a signal translator means on. said vehiclehaving a pair of antennas radiation coupled with the nearest pair ofradiating means along said cable.

5. The system of claim 4 wherein said decouplers comprise: means forseparating the two carrier frequencies into said pair of radiatinglines.

6. The system of claim 4 wherein said decouplers comprise: a pair offilters for separating the carrier frequency from one terminal from thatof the other, and means for connecting the separated carrier frequenciesto separate the ones of said pair of radiating lines.

1. A communication system for a vehicle fol- 'f lowing a routecomprising: a transmitter-receiver at one end of said route fortransmitting signals on one carrier wave at one frequency, anothertransmitter-receiver at the other end of said route for transmittingsignals on another 68 carrier wave at a different frequency. saidcarrier frequencies being of at least a radiation frequency, a cableextending Valong said route between said transmitter-receivers forcarrying said carrier waves, a plurality of transmitter-receiverscoupled to said cable at spaced intervals along said route, eachtransmitter-receiver coupled to said cable having a pair of radiatingmeans along said route extending between it and the radiatmitter-receivers coupled to said cable include means for separating saidcarrier waves and means for receiving and transmitting one of saidcarrier waves to and from one of said radiating 5 means.

10. The system of claim 7 wherein said transmitter-receivers coupled tosaid cable include means'for' separating' said carrier waves, means fortransmitting' one of said separated waves to ylo one of'said pair ofradiating means, and means for transmitting and receiving the other ofsaid separated waves toand from the other of said pair of radiatingmeans.

l1. The system of claim 'I wherein said re- 15 ceiver-transmitterscoupledtosaid cable at spaced intervals along said route include meansfor identifying which of said transmitter-receivers is adjacent saidvehicle along said route.

12. The system of claim 7 wherein said trans- 20 mitter-receiverscoupled to lsaid cable include means for separating said carrier wavesand amplifying the separated frequencies.

13. The system of claim 'l wherein said trans- :hitter-receivers coupledto said cable include 25 means for separating and repeating said wavescarrying modulated signals along said cable.

14. The system'of claim 7 wherein said separate cables are provided -foreach of said carrier waves along said route.

o 15. 'I'he system of claim '7 wherein at least one of the transmittersincludes means for transmitting signals received from one carrier waveto said other carrier wave.

16. A location indication system for vehicles along a route comprising:a transmitter-receiver terminal at one end of said route including meansfor transmitting pulses of a given frequency on a carrier wave, saidfrequency being of a radiation frequency, a cable for carrying saidpulses along said route, a plurality of decouplers at spaced intervalsalong said cable, each of said decouplers having a radiating means alongsaid route extending between it and the radiating means of the nextadjacent decoupler. a signal translator means on said vehicle having anantenna radiation-coupled with the nearest radiating means A along saidcable, and said vehicle including means for receiving said pulses andretransmitting them on a carrier wave of a different frequency back oversaid cable to said terminal, and means in said terminal for receivingsaid retransmitted pulses and indicating the location of said vehiclealong said route with respect to said terminal.

17. The system of claim 16 wherein each of said decouplers along saidcable include means for identifying which one first receives saidretransmitted pulse from said vehicle.

18. The system of claim 16 wherein said signal translator means on saidvehicle includes means $0 for identifying that vehicle from othervehicles along said route.

19. The system of claim 16 wherein said signal translator means on saidvehicle includes means for controlling the retransmission of .saidreceived ing means of the next adjacent radio transmittel pulses foridentifying that vehicle with respect to one of said radiating meansbeing for each of said carrier waves, and a transmitter on said vehiclehaving a pair of antennas radiation coupled with the next pair ofradiating means along said cable.

arating said carrier waves and means for transmitting one of saidseparated waves.

. l" ,10 8. The system of claim 7 wherein said receivers rf coupled tosaid cable comprise: means for sepother vehicles along said route.

20. The system of claim 16 wherein said indieating means in saidterminal includes a cathode ray tube.

2l. The system of claim 16 wherein said indicating means in saidterminal includes a cathode ray tube having a sweep circuit synchronizedby the frequency of transmission of said pulses from said terminal, anda fluorescent screen having a 9. The system of claim 7 wherein saidtrans- 75V scale calibrated to correspond with the length of vehicle,and means for causing said spots 1toilicker in a code signalcorresponding to each of said vehicles along said route.

23. The system of claim 16 wherein said terminal includes means forretransmitting said received pulses for operating indicating means -located at other points along said routes.

24. The system of claim 16 wherein said terminal includes means forretransmitting said re.- ceived pulses for operating indicating means-ineach of the vehicles along said route for indicating the location ofeach of said vehicles along said route as well as therlocation of saidterminal.

25. Ihe system of claim 16 wherein saidindicating means includes acathode ray device for visually indicating the speed and direction ofeach of said vehicles along said route.

26. The system of claim 16 wherein said indicating means includes meansfor indicating the relative speed of said vehicles with respect to saidterminal.

27. A multichannel signal communication system for a vehicle following aroute comprising: a terminal radio transmitter receiver for transmittinga plurality of-trains of interleaved signal modulated pulses and a trainof marker pulses separating like groups ofsignal modulated pulses andtransmitting the resulting combined multichannel pulse wave having atleast a radiation frequency, a cable for carrying said multichannelpulse wave along said route, a plurality f decouplers at spacedintervals along said cable, each decoupler having a radiating meansextendingalong said route between it and the radiating means of the nextadjacent decoupler, and a signai translator means on said vehicle havingan antenna coupled with the nearest radiating means along said cable forreceiving said marker pulses and at least one channel of said signalmodulated pulses.

28. A multichannel signal communication and location indicating 'systemfor' vehicles following a route comprising: a transmitter-receiver atone end of said route fortransmitting a. plurality of signal modulatedpulses on a carrier wave having at least a radiation frequency, anothertransmitter-receiver at the other end of said route for transmitting aplurality of signal modulated pulses on a carrier wave having at least aradiation frequency and different from said first mentioned frequency,said carrier frequency waves also carrying-.marker pulses interleavedbetween similar channel groups of signal modulated pulses and one ofsaid carrier waves carrying locationindicating pulses having a frequencylower than that of said marker pulses, a cable extending between saidend transmitter-receivers and along said route for carrying said carrierwaves, a plurality of decouplers at spaced intervals along said cable,each decoupler having a pair of radiating means extending along saidroute between it and the radiating means oi' the next adjacentdecoupler, one radiating means of each pair for each of said carrierwaves, and a transmitter receiver on said vehicle having a pair ofantennas radiation-coupled withl the nearest pair of radiating meansalong said cable.

29. 'I'he system oi.'v claim 28, wherein said location indicating pulsesare in synchronism with said marker pulses and diil'er therefrom inwidth.

30. The system of claim 28 wherein the frequency of the marker pulsesalong each carrier wave is the same.

wave is dinerent. c

32. The system of claim 28 wherein at least oneof the transmitters insaid system includes means controlled by said location-indication pulsesfor indicating thelocation of said vehicle along said route.

33. The system of claim 28 wherein the transmitten-receiver transmittingthe location-indicating pulse includes means for indicating the positionof the vehicles along said route.

34. The system of claim 28 wherein all said transmitter-receiversincludes means for indicating the location of each vehicle along saidroute in response to the retransmission by each of said vehicles of saidlocation-indicating pulse.

35. 'I'he system of claim 28 wherein the transmitter-receiver on saidvehicle receives the marker pulses from both carrier waves.

36. The system of claim 28 wherein said transmitter-receivers areprovided with means for alternately blocking each other for a givenperiod of time for transmission of received location indicating pulseson their transmitted waves.

37. The system of claim 28 wherein said transmitter-recelvers includemeans for demodulating the signal modulated pulses and means foreliminating any hum due to the location-indicating pulses on theresulting demodulated signal waves.

38. The system of claim 28 wherein said transmitter-receivers on saidvehicles reshape the rcceived location-indicating pulses, retransmit theresulting reshaped pulses, and wherein said terminal receiver has meansfor separating the reshaped pulses from the other and signal modulatedpulses on said carrier waves.

39. The system of claim 28 wherein said transmitter-receiver on saidvehicle includes means for changing the width of the location-indicatingpulses received by said vehicle, retransmits the' resulting reshapedpulses, land wherein said rejceivers have means for width selecting thereshaped pulses and means operated by the resulting selected pulses forindicating simultaneously the position of said vehicle along said route.

40. A multichannel -signal communication and location indicating systemfor a' vehicle following a route comprising: a terminal transmitter andreceiver for transmitting and receiving a plurality of signal modulatedpulses representing a plurality of different signal channels includinglocationindicating pulses, a cable for carrying said pulses along saidroute at a frequency of at least video frequency, a plurality ofdecouplers at spaced intervals along said cable, each having a radiatingmeans extending along said route between rit and the radiating means ofthe next adjacent decoupler, and a signal translator means on saidvehicle having an antenna radiation-coupled with the nearest radiatingmeans along said cable including means for separating the diierentsignal channel on the received pulse wave. means for separating thelocation indication pulses on said wave, and means controlled by theresulting separated location indicating pulses for indicating the 31.The system of claim 28 whereinthe fre quency of the marker pulses alongthe carrier

